The present invention generally relates to medical treatment systems that receive and return fluids to a patient. More particularly, this invention relates to a medical treatment system suitable for use in dialysis and other therapies in which a fluid is withdrawn and then returned to a living body, and flow rates, fluid concentrations, temperature, and other process parameters can be accurately sensed with flow rate sensors.
Hemodialysis and peritoneal dialysis are used to remove impurities from the blood, such as in the treatment of renal failure and various toxic conditions. In hemodialysis, a patient's blood is shunted from the body through a machine for diffusion and ultrafiltration before being returned to the patient's circulation system. Peritoneal dialysis requires access to the peritoneal cavity, and involves the use of a catheter to fill the peritoneal cavity with a dialysis solution. Waste products pass from the blood into the dialysis solution through the peritoneum, and are then removed from the peritoneal cavity when the dialysis solution is drained.
Traditional hemodialysis is performed by accessing the blood stream through an external shunt or arteriovenous fistula. The external shunt is constructed by inserting two cannulas through the skin into a large vein and artery. When performing dialysis the two cannulas are used separately, allowing arterial blood to flow to a dialyzer with which wastes (urea, creatinine, etc.) are removed with a dialysate solution, after which the dialyzed blood is returned to circulation through the cannula in the vein. A blood pump is used to maintain flow through the dialysis system, and various sensors are used to monitor the system, such as to monitor the rate of heparin (anticoagulant) infusion, the conductivity and temperature of the dialysate solution, and blood leak rates in the dialysate solution leaving the dialyzer. Pressure sensors, air bubble detectors, temperature monitors, leak detectors, and conductivity meters have all been used, each usually as a separate individual sensor that often must accommodate the relatively high blood flow rates that must be maintained within the system to avoid clotting. High dialysate flow rates through the dialyzer and the dialysis membrane are also desirable to maximize the removal rate of urea and other wastes. Consequently, accurate flow rate measurement is required, which in the past have included the use of ultrasonic flow sensors, optical sensors, and volumetric containers. Finally, additional sensors, equipment, and procedures have been used to monitor the efficiency and progress of dialysis procedures, such as the slow-flow method, saline-dilution method, blood temperature modules, monitoring urea and hematocrit levels, and the occlusion method.
It would be desirable to improve yet simplify accurate monitoring of dialysis treatments while avoiding clotting and other dialysis-related problems that can occur, including hemorrhaging, hypotension, infection, thrombophlebitis, etc.